1. Field of the Invention
The present invention relates to a communication device and a communication method having a function to suppress power consumption in a standby state.
2. Description of the Related Art
Conventionally, office automation (OA) equipment, such as printers and multifunction peripherals (MFPs) that enable a plurality of functions including a printing function, a scanning function, a copying function, and a facsimile (FAX) function in one housing has been designed to reduce power consumption by, when a device is not used for more than a predetermined time period, making only a part of the functions in the device enabled and stopping supplying power to a section whose function is made disabled. Hereinafter, a state in which power consumption is reduced in this manner when a device is not used for more than a predetermined time period is referred to as a standby state.
Examples of a method for supplying power in the standby state include a method using an energy device that generates electricity, such as a solar cell, in addition to a method for supplying power from a commercial power supply, which has been conventionally employed. By supplying power using the energy device in the standby state, power consumption can be reduced more effectively. In the standby state, it is preferable to reduce power consumption as much as possible even in the case where power is supplied from the energy device besides the case where power is supplied from the commercial power supply.
A function made enabled in the standby state and power consumption in the standby state are in a trade-off relationship. For example, an MFP and a printer described above typically have a communication function through a network. In such a device, if the communication function through the network is made disabled in the standby state, the device virtually disappears from the network.
While the device disappears from the network, even if a packet is transferred to the device via the network, the packet is not received by the device unless the device returns to a normal state automatically. In this case, a user needs to cause the device to return to the normal state manually, for example. Therefore, it is significantly effective to make the network communication function enabled in the standby state, and to make the device capable of responding to the network.
In recent years, data transfer technologies over networks have been developed, and network standards that support a higher transfer rate have become popular. In Ethernet (registered trademark), for example, compared with conventional 100BASE-x standard at a transfer rate of 100 Mbps, 1000BASE-x standard at a transfer rate of 1 Gbps and 10GBASE-x standard at a transfer rate of 10 Gbps have become popular. Note that “-x” in “100BASE-x” and the like indicates an aspect of a communication path, and stands for “T”, “TX”, or “FX”, for example.
As described above, associated with an increase in a data transfer rate over a network, power consumption in a communication interface corresponding thereto tends to increase. In responding to the increase in power consumption, it is required to reduce power consumption in a communication interface by monitoring traffic on the network and controlling a function of the communication interface according to the traffic.
Institute of Electrical and Electronics Engineers (IEEE) has established IEEE 802.3az as one of communication standards capable of controlling a function of a communication interface according to the traffic. The IEEE 802.3az is also referred to as Energy Efficient Ethernet (EEE, which is a registered trademark). The IEEE 802.3az specifies that traffic of a network is monitored, and if no traffic is generated for a certain period of time, power-saving control is applied to a physical layer (PHY layer), which is the lowest layer, and to a data link layer (media access control (MAC) layer), which is a layer upper than the PHY layer.
According to the IEEE 802.3az, for example, by taking account of the traffic of the network, if no communication is performed for a certain period of time, reduction in power consumption is attempted by stopping a clock for a chip in the MAC layer to make the function of the MAC layer disabled. Furthermore, even if no communication is performed for the certain period of time, a packet can be received in the standby state by enabling the function of the PHY layer. There is a method called low power idle (LPI) for controlling, depending on presence or absence of communications, the MAC layer by switching the function thereof between enabled and disabled. Hereinafter, a state in which no communication is performed for a certain period of time that is a threshold for making the function of the MAC layer disabled is referred to as an LPI state.
In relation to the IEEE 802.3az, Japanese Patent Application Laid-open No. 2010-268024 discloses a technology for enabling to identify silent failure, which can occur on an Ethernet (registered trademark) network to which the IEEE 802.3az is applied and which may not be recognized by an operation manager, from a remote network operation management system reliably and promptly.
Japanese Patent Application Laid-open No. 2010-213259 discloses a technology for enabling to reduce power consumption by putting a user device into a sleep mode through Ethernet (registered trademark) to which the IEEE 802.3az is applied to allow a transmitter and a receiver of the user device to power off for a predetermined time period (sleep time).
Before the establishment of the IEEE 802.3az, however, even a system considering a network response in the standby state has had no measure to suppress power consumption if no traffic is generated on a network. In other words, conventionally, in a system capable of responding to a network in the standby state, control has been performed such that the system is caused to return from the standby state to the normal state at a required timing by filtering packets transmitted via the network. However, no control for reducing power consumption according to a monitoring result of traffic has been performed before the establishment of the IEEE 802.3az.
Furthermore, power consumption in a communication interface increases as the link rate increases even if the IEEE 802.3az is applied thereto. If the link rate is in the 1000BASE class (1 Gbps), for example, the power consumption increases by approximately 50 mW to 100 mW compared with the case where the link rate is in the 100BASE class (100 Mbps). For this reason, if a communication interface is used at a link rate of the 1000BASE class, it may be difficult to use an energy device, such as a solar cell, for supplying power in the standby state.
To address this problem, the link rate may be degraded from the 1000BASE-x class to the 100BASE-x class in the standby state. In accordance with the IEEE 802.3az standard, however, there has been a problem in that the link rate fails to be changed after the device shifts to the LPI state. This problem is common to Japanese Patent Application Laid-open No. 2010-268024 and Japanese Patent Application Laid-open No. 2010-213259.
As described above, in a communication interface usable at a higher link rate, such as 1000BASE-x, it is required to make a network response enabled and to achieve further reduction in power consumption in the standby state.
In view of the problems described above, there is a need to make a network response enabled and to achieve further reduction in power consumption of a communication interface in a standby state.